Java 7 ClassLoader performance improvements

Use Java 7 `registerAsParallelCapable` and `getClassLoadingLock` methods
when possible. This should improve performance when running on JDK 7+
whilst still remaining JDK 6 compatible.

Closes gh-1284

spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/LaunchedURLClassLoader.java

@@ -36,8 +36,19 @@ import org.springframework.boot.loader.jar.JarFile;
  */
 public class LaunchedURLClassLoader extends URLClassLoader {
 
+	static {
+		try {
+			ClassLoader.registerAsParallelCapable();
+		}
+		catch (NoSuchMethodError ex) {
+			// Not available on earlier JDKs
+		}
+	}
+
 	private final ClassLoader rootClassLoader;
 
+	private final LockProvider lockProvider;
+
 	/**
 	 * Create a new {@link LaunchedURLClassLoader} instance.
 	 * @param urls the URLs from which to load classes and resources
@@ -46,6 +57,17 @@ public class LaunchedURLClassLoader extends URLClassLoader {
 	public LaunchedURLClassLoader(URL[] urls, ClassLoader parent) {
 		super(urls, parent);
 		this.rootClassLoader = findRootClassLoader(parent);
+		this.lockProvider = createLockProvider();
+	}
+
+	private LockProvider createLockProvider() {
+		try {
+			ClassLoader.class.getMethod("getClassLoadingLock", String.class);
+			return new Java7LockProvider();
+		}
+		catch (NoSuchMethodException ex) {
+			return new LockProvider();
+		}
 	}
 
 	private ClassLoader findRootClassLoader(ClassLoader classLoader) {
@@ -126,7 +148,7 @@ public class LaunchedURLClassLoader extends URLClassLoader {
 	@Override
 	protected Class<?> loadClass(String name, boolean resolve)
 			throws ClassNotFoundException {
-		synchronized (this) {
+		synchronized (this.lockProvider.getLock(this, name)) {
 			Class<?> loadedClass = findLoadedClass(name);
 			if (loadedClass == null) {
 				Handler.setUseFastConnectionExceptions(true);
@@ -222,4 +244,27 @@ public class LaunchedURLClassLoader extends URLClassLoader {
 		}
 	}
 
+	/**
+	 * Strategy used to provide the synchronize lock object to use when loading classes.
+	 */
+	private static class LockProvider {
+
+		public Object getLock(LaunchedURLClassLoader classLoader, String className) {
+			return classLoader;
+		}
+
+	}
+
+	/**
+	 * Java 7 specific {@link LockProvider}.
+	 */
+	private static class Java7LockProvider extends LockProvider {
+
+		@Override
+		public Object getLock(LaunchedURLClassLoader classLoader, String className) {
+			return classLoader.getClassLoadingLock(className);
+		}
+
+	}
+
 }